According to the original Greek, the soul and the spirit are not the same thing. When you say Jesus' human spirit is fused with His divine spirit, it is more correct to say that His Spirit is fused with His soul. We do not have two spirits, just one spirit and one soul. Both words are associated with Jesus' construction so to speak. I keep my definition confined to the usage of the words in the scripture that describe Jesus' construction as a human. He had a body, soul and spirit. His Spirit is the Holy Spirit and His soul was begotten to take our sins. There are no other words in scripture associated with Jesus physiology.
I agree that the soul and spirit are not the same thing. This is a reason why I say that Jesus has a human body, soul and spirit. If you REPLACE the human spirit with the Holy Spirit, then how do you say that he is fully human? I'm not comfortable with a component of his humanity being REPLACED and still saying He is fully human. How do you get away with that in all honesty?
Do you chuck Luke 23:46 out? "Father into thy hands I commend by pneuma (spirit)". He didn't say "soul".